There is a known outlet seal for the cathode bars of an aluminum electrolytic cell (USSR Inventor's Certificate No. 865992, IPC C 25 C 3/16, 1981), containing a branch pipe narrowing in the direction away from the shell and connected to the cathode shell, a thrust ring connected to the outer end of the branch pipe, a sealing gland, a cathode bar, a flange joined to the cathode bar, and a layer of alumina.
The drawback of the known seal is that the sealing gland and the layer of alumina are gas permeable. Also during the period of firing and startup of the aluminum electrolytic cell and in the process of operation the cathode bar shifts along its axis due to thermal expansion, and the cathode bar shifts transversely to its axis as a result of sodium expansion of the carbon portion of the lining. This leads to disruption of the tightness of the seal due to the inability of the sealing gland to compensate for the transverse displacement of the cathode bar and the wear caused by its axial displacement. Air gets in through the sealing gland and the layer of alumina and disrupts the tightness of the carbon side lining, oxidizing and destroying it. This lowers the service life of the aluminum electrolytic cell and quite often is the cause of melt breakthrough and leakage through the apertures for passage of the cathode bars that are cut out from the lengthwise walls of the cathode shell. Furthermore, one should mention the labor intensity and length of time to perform the installation work involved in filling the free space around the cathode bar with a seal.
There is a known outlet seal for the cathode bars of an aluminum electrolytic cell (RF patent No. 2281347, IPC C25C 3/08, 2006), containing a plate with an opening, situated on the inside of the apertures for passage of the cathode bars that are made in the cathode shell, and a sylphon hermetically connected by one end to the cathode bar and by the other to the cathode shell. In this device, the plate with opening is seated on the cathode bar with ability to move along its axis and cover the apertures.
The drawbacks of the known seal are:
since the cathode bar is a rolled product, its surface has irregularities and consequently aggressive gases (especially HF) pass inside the sylphon in the gap between the cathode bar and the plate during the firing and startup of the electrolytic cell and bring about corrosion and loss of tightness;
the sylphon due to its principle of operation has a developed surface area of folds and an internal space volume and therefore if it is filled with sealant it has an elevated outlay of sealant, i.e., a high cost price and labor intensity;
the sylphon has a fixed connection of both its ends, and consequently it is not possible to add elastic sealant inside the sylphon during its operation, if necessary.
The closest to the present disclosure in its set of essential features is a seal (RF patent No. 2108414, IPC C25C 3/08, 1998) containing a sealing means around the cathode bar, a metal box with two openings joined to the cathode shell with apertures for passage of the cathode bars, and a layer of material allowing the cathode bar to slide relative to the sealing means.
The drawback of the prototype is that during the period of firing and startup of the aluminum electrolytic cell and in the process of operation the cathode bar shifts along its axis due to thermal expansion, and the cathode bar shifts transversely to its axis as a result of sodium expansion of the carbon portion of the lining. Since the cathode bar is a rolled product, its surface has irregularities. Due to the axial displacement between the cathode bar and the solidified sealing means, gaps are formed. As a result of the transverse displacement of the cathode bar, destruction of the solidified sealing means occurs. Air gets in through the gaps forming in the lateral carbon lining, oxidizing and destroying it. This lowers the service life of the aluminum electrolytic cell and quite often is the cause of melt breakthrough and leakage through the apertures for passage of the cathode bars that are cut out from the lengthwise walls of the cathode shell. Furthermore, one should mention the labor intensity and length of time to perform the installation work involved in filling the free space around the cathode bar with a seal.